Perfluorooctanoic acid affects the activity of the hepatocyte nuclear factor 4 alpha (HNF4α).

Perfluorooctanoic acid (PFOA) is an industrial chemical that is a global contaminant of water, soil and foodstuff. Numerous animal studies have revealed that PFOA has embryotoxic and hepatotoxic effects in rodents. On the molecular level, the adverse effects of PFOA have been correlated with the PFOA-mediated activation of peroxisome proliferator-activated receptor alpha (PPARα), however, the toxicological relevance of this mode of action for humans is under debate. In this study, a proteomic approach was chosen to screen for molecular targets affected by PFOA in human liver cells. Treatment of the human liver cell line HepG2 with 25 µM PFOA resulted in 51 deregulated proteins in a two-dimensional gel experiment, and 36 of these proteins were identified by mass spectrometry. Network analysis revealed that these proteins are primarily involved in lipid metabolism and cancer. The hepatocyte nuclear factor 4α (HNF4α), but not PPARα, was the key regulator of the network. Indeed, subsequent western blot analysis revealed that the amount of HNF4α as well as of its target HNF1α was downregulated in PFOA-treated HepG2 cells. Moreover, PFOA was shown to inhibit HNF4α-dependent gene transcription. Thus, this study provides first experimental evidence that HNF4α is negatively affected by PFOA.

Glutathione S-transferase expression and isoenzyme composition during cell differentiation of Caco-2 cells.

The human colon adenocarcinoma cell line Caco-2 is frequently used to study human intestinal metabolism and transport of xenobiotica. Previous studies have shown that both Caco-2 cells and human colon cells constitutively express the multigene family of detoxifying enzymes glutathione S-transferases (GSTs), particularly GST alpha and GST pi. GSTs may play a fundamental role in the molecular interplay between phase I, II enzymes and ABC-transporters. The gut fermentation product, butyrate, can modulate the potential for detoxification. The aim of this study was to investigate the basal expression of further cytosolic GSTs in Caco-2 cells during cell differentiation. In addition, a comparison was made with expression levels in MCF-7 and HepG2, two other cell types with barrier functions. Finally, the butyrate-mediated modulation of gene and protein expression was determined by real time PCR and western blot analysis. In Caco-2, gene and protein expression levels of GST alpha increased during cell differentiation. High levels of GSTO1 and GSTP1 were constantly expressed. No expression of GSTM5 and GSTT1 was detected. HepG2 expressed GSTO1 and MCF-7 GSTZ1 most intensively. No expression of GSTA5, GSTM5, or GSTP1 was detected in either cell. Incubation of Caco-2 cells with butyrate (5 mM) significantly induced GSTA1 and GSTM2 in proliferating Caco-2 cells. In differentiated cells, butyrate tended to increase GSTO1 and GSTP1. The results of this study show that a differentiation-dependent expression of GSTs in Caco-2 cells may reflect the in vivo situation and indicate the potential of butyrate to modify intestinal metabolism. GSTA1-A4 have been identified as good markers for cell differentiation. The Caco-2 cell line is a useful model for assessing the potential of food-related substances to modulate the GST expression pattern.